U.S. patent number 8,247,088 [Application Number 12/200,163] was granted by the patent office on 2012-08-21 for emitting complex for electroluminescent devices.
This patent grant is currently assigned to Global OLED Technology LLC. Invention is credited to Joseph C. Deaton, David J. Giesen, Xiaofan Ren.
United States Patent |
8,247,088 |
Ren , et al. |
August 21, 2012 |
Emitting complex for electroluminescent devices
Abstract
An OLED device including a cathode, an anode, and having
therebetween a phosphorescent light-emitting layer that contains a
light-emitting organometallic complex including a precious metal, a
first ligand including an imidazole group and a second nitrogen
heterocycle group, and at least one second different ligand.
Inventors: |
Ren; Xiaofan (Rochester,
NY), Deaton; Joseph C. (Rochester, NY), Giesen; David
J. (Webster, NY) |
Assignee: |
Global OLED Technology LLC
(Wilmington, DE)
|
Family
ID: |
41724286 |
Appl.
No.: |
12/200,163 |
Filed: |
August 28, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100052516 A1 |
Mar 4, 2010 |
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Current U.S.
Class: |
428/690;
257/E51.044; 252/301.16; 313/506; 257/40; 257/102; 546/4; 313/504;
548/103; 428/917 |
Current CPC
Class: |
H05B
33/14 (20130101); C09K 11/06 (20130101); H01L
51/0085 (20130101); C09K 2211/185 (20130101); C09K
2211/1029 (20130101); H01L 51/0094 (20130101); C09K
2211/1044 (20130101); H01L 51/5016 (20130101) |
Current International
Class: |
H01L
51/54 (20060101); C09K 11/06 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
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Other References
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|
Primary Examiner: Chriss; Jennifer
Assistant Examiner: Wilson; Michael H
Attorney, Agent or Firm: McKenna Long & Aldridge LLP
Claims
The invention claimed is:
1. An OLED device comprising a cathode, an anode, and having
therebetween a phosphorescent light-emitting layer that contains a
light-emitting organometallic complex represented by Formula 2:
##STR00021## wherein the device emits blue light.
2. The OLED device of claim 1 wherein the light-emitting
organometallic complex is a dopant compound disposed in a host
material.
3. The OLED device of claim 2 wherein the dopant compound is
present in an amount of up to 15% by weight based on the host
material.
4. The OLED device of claim 2 wherein the host material includes a
nitrogen heterocyclic host compound.
5. The OLED device of claim 2 wherein the host material includes an
organic phosphineoxide host compound.
6. The OLED device of claim 2 wherein the host material includes an
organosilane host compound.
7. An OLED device comprising a cathode, an anode, and having
therebetween a phosphorescent light-emitting layer that contains a
light-emitting organometallic complex represented by Formula 3:
##STR00022## wherein the device emits blue light.
8. The OLED device of claim 7 wherein the light-emitting
organometallic complex is a dopant compound disposed in a host
material.
9. The OLED device of claim 8 wherein the dopant compound is
present in an amount of up to 15% by weight based on the host
material.
10. The OLED device of claim 8 wherein the host material includes a
nitrogen heterocyclic host compound.
11. The OLED device of claim 8 wherein the host material includes
an organic phosphineoxide host compound.
12. The OLED device of claim 8 wherein the host material includes
an organosilane host compound.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
Reference is made to commonly assigned U.S. patent application Ser.
No. 11/141,092 filed May 31, 2005, (now U.S. Patent Application
Publication No. 2006/0269784) entitled "Light-Emitting Device
Containing Bis-Phosphineoxide Compounds" by Ren; U.S. patent
application Ser. No. 11/254,108 filed Oct. 19, 2005 (now U.S.
Patent Application Publication No. 2007/0087219), entitled
"Electroluminescent Device" by Ren et al.; the disclosures of which
are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to an organic light emitting diode
(OLED) electroluminescent (EL) device including a light-emitting
layer containing an organometallic complex that can provide
desirable electroluminescent properties.
BACKGROUND OF THE INVENTION
While organic electroluminescent (EL) devices have been known for
over two decades, their performance limitations have represented a
barrier to many desirable applications. In simplest form, an
organic EL device includes an anode for hole injection, a cathode
for electron injection, and an organic medium sandwiched between
these electrodes to support charge recombination that yields
emission of light. These devices are also commonly referred to as
organic light-emitting diodes, or OLEDs. Representative of earlier
organic EL devices are Gurnee et al. U.S. Pat. No. 3,172,862,
issued Mar. 9, 1965; Gurnee U.S. Pat. No. 3,173,050, issued Mar. 9,
1965; Dresner, "Double Injection Electroluminescence in
Anthracene", RCA Review, Vol. 30, pp. 322-334, 1969; and Dresner
U.S. Pat. No. 3,710,167, issued Jan. 9, 1973. The organic layers in
these devices, usually composed of a polycyclic aromatic
hydrocarbon, were very thick (much greater than 1 .mu.m).
Consequently, operating voltages were very high, often
>100V.
More recent organic EL devices include an organic EL element
consisting of extremely thin layers (e.g. <1.0 .mu.m) between
the anode and the cathode. Herein, the term "organic EL element"
encompasses the layers between the anode and cathode electrodes.
Reducing the thickness lowered the resistance of the organic layer
and has enabled devices that operate at much lower voltage. In a
basic two-layer EL device structure, described first in U.S. Pat.
No. 4,356,429, one organic layer of the EL element adjacent to the
anode is specifically chosen to transport holes, and therefore is
referred to as the hole-transporting layer, and the other organic
layer is specifically chosen to transport electrons, and referred
to as the electron-transporting layer. Recombination of the
injected holes and electrons within the organic EL element results
in efficient electroluminescence.
There have also been proposed three-layer organic EL devices that
contain an organic light-emitting layer (LEL) between the
hole-transporting layer and electron-transporting layer, such as
that disclosed by Tang et al [J. Applied Physics, Vol. 65, Pages
3610-3616, 1989]. The light-emitting layer commonly consists of a
host material doped with a guest material. Still further, there has
been proposed in U.S. Pat. No. 4,769,292 a four-layer EL element
including a hole-injecting layer (HIL), a hole-transporting layer
(HTL), a light-emitting layer (LEL) and an electron
transport/injection layer (ETL). These structures have resulted in
improved device efficiency.
Many emitting materials that have been described as useful in an
OLED device emit light from their excited singlet state by
fluorescence. The excited singlet state is created when excitons
formed in an OLED device transfer their energy to the excited state
of a light-emitting dopant. However, it is generally believed that
only 25% of the excitons created in an EL device are singlet
excitons. The remaining excitons are triplet, which cannot readily
transfer their energy to the singlet excited state of a dopant.
This results in a large loss in efficiency since 75% of the
excitons are not used in the light emission process.
Triplet excitons can transfer their energy to a dopant that has a
triplet excited state that is low enough in energy. If the triplet
state of the dopant is emissive it can produce light by
phosphorescence. In many cases, singlet excitons can also transfer
their energy to the lowest singlet excited state of the same
dopant. The singlet excited state can often relax, by an
intersystem crossing process, to the emissive triplet excited
state. Thus, it is possible, by the proper choice of host and
dopant, to collect energy from both the singlet and triplet
excitons created in an OLED device and to produce a very efficient
phosphorescent emission.
Fac-Tris(2-Phenylpyridinato-N,C.sup.2')Iridium(III) (Ir(ppy).sub.3)
strongly emits green light from a triplet excited state owing to
the large spin-orbit coupling of the heavy atom and to the lowest
excited state, which is a charge transfer state having a Laporte
allowed (orbital symmetry) transition to the ground state (K. A.
King, P. J. Spellane, and R. J. Watts, J. Am. Chem. Soc., 107, 1431
(1985), M. G. Colombo, T. C. Brunold, T. Reidener, H. U. Gudel, M.
Fortsch, and H.-B. Burgi, Inorg. Chem., 33, 545 (1994)). It is
reported that, when used as a dopant in a EL device, this material
affords an internal quantum efficiency of greater than 85%. This
high efficiency can result from collecting energy from both the
singlet and triplet excited states of the host
(3-phenyl-4-(1'-naphthyl)-5-phenyl-1,2,4-triazole (TAZ) was the
host material). Highly efficient red electrophosphorescence has
also been reported, using
bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C.sup.3)iridium(acetylacetonat-
e) [Btp.sub.2Ir(acac)] as the dopant (Adachi, C., Lamansky, S.,
Baldo, M. A., Kwong, R. C., Thompson, M. E., and Forrest, S. R.,
App. Phys. Lett., 78, 1622-1624 (2001)).
Small-molecule, vacuum-deposited OLEDs having high efficiency have
also been demonstrated with Ir(ppy).sub.3 as the dopant and
4,4'-N,N'-dicarbazole-biphenyl (CBP) as the host (M. A. Baldo, S.
Lamansky, P. E. Burrows, M. E. Thompson, S. R. Forrest, Appl. Phys.
Lett., 75, 4 (1999), T. Tsutsui, M.-J. Yang, M. Yahiro, K.
Nakamura, T. Watanabe, T. Tsuji, Y. Fukuda, T. Wakimoto, S.
Miyaguchi, Jpn. J. Appl. Phys., 38, L1502 (1999)). The layer
containing the dopant and host was deposited adjacent to a
hole-blocking layer, 2,9-dimethyl-4,7-diphenyl-phenanthroline
(bathocuproine, BCP). Other device structures for generating
electrophosphorescence have also been documented, for example see
C. Adachi, M. A. Baldo, S. R. Forrest, and M. E. Thompson, Appl.
Phys. Lett., 77, 904 (2000).
The emission wavelengths of cyclometallated Ir(III) complexes of
the type IrL.sub.3 and IrL.sub.2L', such as the green-emitting
fac-tris(2-phenylpyridinato-N,C.sup.2')Iridium(III) and
bis(2-phenylpyridinato-N,C.sup.2')Iridium(III)(acetylacetonate) can
be shifted by substitution of electron donating or withdrawing
groups at appropriate positions on the cyclometallating ligand L,
or by choice of different heterocycles for the cyclometallating
ligand L. The emission wavelengths can also be shifted by choice of
the ancillary ligand L'. Examples of red emitters are the
bis(2-(2'-benzothienyl)pyridinato-N,C.sup.3')Iridium(III)(acetylacetonate-
) and tris(2-phenylisoquinolinato-N,C.sup.8')Iridium(III). A
blue-emitting example is
bis(2-(4',6'-diflourophenyl)-pyridinato-N,C.sup.2')Iridium(III)(picolinat-
e).
Other important phosphorescent dopants include cyclometallated
Pt(II) complexes such as
cis-bis(2-phenylpyridinato-N,C.sup.2')platinum(II),
cis-bis(2-(2'-thienyl)pyridinato-N,C.sup.3')platinum(II),
cis-bis(2-(2'-thienyl)quinolinato-N,C.sup.5')platinum(II), or
(2-(4,6-diflourophenyl)pyridinato-N,C.sup.2')platinum (II)
acetylacetonate. Pt(II) porphyrin complexes such as
2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphine platinum(II) are
also useful phosphorescent dopants.
Without being limited to a particular theory, phosphorescence can
be found among transition metal ion octahedral complexes having
d.sup.6 electron configuration and square planar complexes having
d.sup.8 electron configuration, each also having as the
lowest-energy excited state a metal-to-ligand charge transfer
transition or a ligand pi-pi* transition that is capable of mixing
with a nearby metal-to-ligand charge transfer. Suitable transition
metal ions for phosphorescent complexes include preferably the
second or third transition series, or more preferably the third
transition series (Hf, Nb, W, Re, Os, Ir, Pt, Au).
Other examples of phosphorescent compounds include compounds having
interactions between atoms having d.sup.10 electron configuration,
such as Au.sub.2(dppm)Cl.sub.2 (dppm=bis(diphenylphosphino)methane)
(Y. Ma et al, Appl Phys. Lett., 74, 1361 (1998)). Still other
examples of phosphorescent dopants include coordination complexes
of the trivalent lanthanides such as Tb.sup.3- and Eu.sup.3+ (J.
Kido et al, Appl. Phys. Lett., 65, 2124 (1994)). While these latter
dopants do not have triplets as the lowest excited states, their
optical transitions do involve a change in spin state of 1 and
thereby can harvest the triplet excitons in OLED devices.
Phosphorescent dopants are also described in WO 00/57676, WO
00/70655, WO 01/41512 A1, WO 02/15645 A1, WO 01/93642 A1, WO
01/39234 A2, WO 02/071813 A1, EP 1 239 526 A2, EP 1 238 981 A2, EP
1 244 155 A2, WO 02/074015 A2, JP 2003 073387A, JP 2003 073388A, JP
2003 059667A, JP 2003 073665A, U.S. Pat. Nos. 6,458,475 B1;
6,451,455 B1; 6,239,085 B1; 6,413,656 B1; 6,515,298 B2; 6,451,415
B1; 6,097,147; 6,573,651 B2; U.S. Patent Application Publication
Nos. 2002/0197511 A1; 2003/0124381 A1; 2003/0072964 A1;
2003/0068528 A1; 2003/0059646 A1; 2003/0054198 A1; 2003/0017361 A1;
2002/0100906 A1; 2003/0068526 A1; 2003/0068535 A1; 2003/0141809 A1;
2003/0040627 A1; 2002/0121638 A1, and 2002/0121638 A1.
In a similar fashion, high efficiency polymer OLEDs containing
phosphorescent dopants, such as Ir(ppy).sub.3, have also been
reported, for example, see M.-J. Yang and T. Tsutsui, Jpn. J. Appl.
Phys., 39, L828 (2000).
Suitable host molecules for phosphorescent dopants must have the
energy of their triplet states about equal to or above that of the
phosphorescent dopant in order that the triplet exciton can be
transferred efficiently from the host to the phosphorescent dopant.
However, the band gap of the host should not be chosen so large as
to cause an unacceptable increase in the drive voltage of the OLED.
Suitable host types are described in WO 00/70655 A2; WO 01/39234
A2; WO 01/93642 A1; WO 02/074015 A2; and WO 02/15645 A1. Suitable
hosts include certain aryl amines and carbazole compounds.
In addition to suitable hosts, an OLED device employing a
phosphorescent dopant often requires at least one exciton- or
hole-blocking layer to help confine the excitons or electron-hole
recombination centers to the light-emitting layer including the
host and dopant. In one embodiment, such a blocking layer would be
placed between the electron-transporting layer and the
light-emitting layer. In this case, the ionization potential of the
blocking layer should be such that there is an energy barrier for
hole migration from the host into the electron-transporting layer,
while the electron affinity should be such that electrons pass more
readily from the electron-transporting layer into the
light-emitting layer including host and dopant. It is further
desired, but not absolutely required, that the triplet energy of
the blocking material be greater than that of the phosphorescent
dopant. Suitable hole-blocking materials are described in WO
00/70655 A2 and WO 01/93642 A1. Two examples of useful materials
are bathocuproine (BCP) and
bis(2-methyl-8-quinolinolato)(4-phenylphenolato)Aluminum(III)
(BAlQ).
Notwithstanding these developments, there remains a need for new
organometallic materials that will function as phosphorescent
emitters, especially in the blue-emitting region. To date, most of
the phosphorescent complexes developed for OLED applications have
emission spectra with peaks in the red and green region. U.S.
Patent Application Publications Nos. 2002/0134984A1 and
2004/0068132A1 also disclose iridium complexes that emit in the
blue region, even though the colors are not saturated. Recently, B.
W. D'Andrade, J.-Y Tsai, C. Lin, M. S. Weaver, P. B. Mackenzie, J.
Brown, "Efficient White Phosphorescent Organic Light-Emitting
Devices," SID Symposium Digest, Vol. 38, pp. 1026-1029, 2007 have
reported a sky-blue phosphorescent OLED with an operational
lifetime of 15,000 hr. at an initial brightness of 200 cd/m.sup.2
and 9.5% external quantum efficiency. However, with CIE coordinates
of (0.16, 0.37), this material is not a sufficiently saturated blue
for commercial full-color applications. Research on higher
triplet-energy emitters has been reported. These emitters are often
iridium complexes that have two cyclometalated (C^N) ligands and
one bidentate ancillary ligand (N^N) (J. Li, P. I. Djurovich, B. D.
Alleyne, M. Yousufuddin, N. N. Ho, J. C. Thomas, J. C. Peters, R.
Bau, M. E. Thompson, "Synthetic Control of Excited-State Properties
in Cyclometalated Ir(III) Complexes Using Ancillary Ligands,"
Inorg. Chem., Vol. 44, pp. 1713-1727, 2005). The (N^N) ancillary
ligands are believed to render these blue phosphors unstable in
devices. To date, the design and synthesis of efficient "deep blue"
phosphorescent emitters remains one of the most challenging tasks
in the OLED community.
Therefore, there remains a need for new efficient phosphorescent
materials, particularly materials that produce their emission in
the blue region of the visible spectrum. It is a problem to be
solved to provide new blue phosphorescent emitting materials that
can function under practical operating conditions in an OLED
device. Desirably, such a material can be developed to improve on
device efficiency and operational stability.
SUMMARY OF THE INVENTION
There is a need for new phosphorescent emitting materials useful in
an OLED device.
This object is achieved by an OLED device comprising a cathode, an
anode, and having therebetween a phosphorescent light-emitting
layer that contains a light-emitting organometallic complex
comprising a precious metal, a first ligand comprising an imidazole
group and a second nitrogen heterocycle group, and at least one
second different ligand.
This object is also achieved by an OLED device comprising a
cathode, an anode, and having therebetween a phosphorescent
light-emitting layer that contains a light-emitting homoleptic tris
organometallic complex comprising iridium and a
C,N-cyclometallating ligand comprising an imidazole group and a
second nitrogen heterocycle group, wherein the organometallic
complex has a facial orientation and an emission maximum at a
wavelength shorter than 480 nm.
It is an advantage of this invention that it provides a blue
emitter with improved color and high efficiency for an OLED
device.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a cross-section of a typical OLED device in which this
invention can be used;
FIG. 2 a comparison of some organometallic complexes useful in this
invention;
FIG. 3 shows an NMR spectrum of a facial tris homoleptic
organometallic complex useful in this invention; and
FIG. 4 shows an emission spectrum for an OLED device of this
invention.
DETAILED DESCRIPTION OF THE INVENTION
In one embodiment, this invention includes an OLED device including
a cathode, an anode, and having therebetween a phosphorescent
light-emitting layer that contains a light-emitting organometallic
complex including a precious metal, a first ligand including an
imidazole group and a second nitrogen heterocycle group, and at
least one second different ligand. A first ligand that is useful
for the practice of this invention includes an imidazole group,
that is, a five-membered unsaturated ring containing two nitrogen
atoms in the 1 and 3 positions, and a second nitrogen heterocycle
group attached to the imidazole ring at the 1-position of the
imidazole ring. It is desirable, but not necessary, that the
imidazole ring system be further substituted with substituents at
the 4 and 5 positions. Usefully, the substituents can form a ring
group, and desirably the ring group is a five or six-membered
aromatic ring. Other substituents can be used on the ring group, or
the second heterocycle group, or both. Illustrative examples of
useful ligands are shown below.
##STR00001##
An OLED device can be constructed including a cathode, an anode,
and having therebetween a phosphorescent light-emitting layer that
contains a light-emitting organometallic complex including a
precious metal, a first ligand as described above, and at least one
second different ligand. The light-emitting organometallic complex
can be represented by certain embodiments, which will be further
described, of Formula (1),
##STR00002## wherein:
M is a 4- or 6-coordinate precious metal;
R.sup.1 and R.sup.2 represent independently selected substituent
groups, provided that R.sup.1 and R.sup.2 can form a ring
group;
Ar represents the groups necessary to complete a substituted or
unsubstituted aromatic group that forms the second nitrogen
heterocycle group;
L and L' are different second ligands; and
m+n+o=2 for a 4-coordinate metal and 3 for a 6-coordinate metal,
provided that m>0 and at least one of n and o are greater than
zero.
Examples of independently selected substituent groups R.sup.1 and
R.sup.2 include phenyl, tolyl, and alkyl such as methyl and ethyl.
In one desirable embodiment R.sup.1 and R.sup.2 form a ring group,
desirably an aromatic ring, such as a substituted or unsubstituted
benzene ring group. Illustrative examples of R.sup.1 and R.sup.2
are shown below.
##STR00003##
M is a coordinated precious metal selected from the group
consisting of Ir, Rh, Ru, Pt, Pd, and Os. In one suitable
embodiment, M represents Ir or Rh, and more desirably M represents
Ir. m is 1 or 2 and m+n+o is 3 when M is Ir, Ru, or Rh, and m is 1
and m+n+o is 2 when M is Pt or Pd.
Desirably, L and L' represent bidentate ligands. For example, L and
L' can represent carbonyl-substituted groups such as an
acetylacetonate group, a hexafluoroacetylacetonate group, or a
salicylaldehyde group. L and L' can also represent acid derivatives
of formula R.sup.aCO.sub.2.sup.-, wherein R.sup.a can be
substituted or unsubstituted aryl, such as phenyl or tolyl, or
substituted or unsubstituted alkyl, such as methyl or butyl.
Examples of desirable bidentate acid derivatives are picolinic acid
and 3-bromopicolinic acid. L and L' can also represent substituted
or unsubstituted phenylpyridyl ligands. In one useful embodiment,
at least one of L and L' is a C,N-cyclometallating ligand. One such
useful C,N-cyclometalating ligand is a phenylpyridyl ligand. In one
such embodiment, the organometallic complex has the structure of
Formula (2):
##STR00004##
In another useful embodiment, the least one C,N-cyclometallating
ligand is a difluorophenylpyridyl ligand. In one such embodiment,
the organometallic complex has the structure of Formula (3):
##STR00005##
Other useful organometallic complex compounds of this invention
include:
##STR00006## ##STR00007## ##STR00008## ##STR00009##
Desirable complexes of this invention exhibit blue light emission.
Facial isomers are desirable for improved blue emission. Meridianal
isomers typically give a broadened and red-shifted emission
relative to that of the corresponding facial isomer (A. B. Tamayo,
et al., J. Am. Chem. Soc., 125, 7377, 2003). Facial isomers are
generally preferred over meridianal isomers because the latter
typically give lower phosphorescent quantum yields in addition to
the broad and red-shifted emission.
In another embodiment, this invention includes an OLED device
including a cathode, an anode, and having therebetween a
phosphorescent light-emitting layer that contains a light-emitting
homoleptic tris organometallic complex including iridium and three
identical C,N-cyclometallating ligands including an imidazole group
and a second nitrogen heterocycle group, wherein the organometallic
complex has a facial orientation with an emission maximum at a
wavelength shorter than 480 nm. The organometallic complex can be a
facial iridium complex of compound 4:
##STR00010## wherein X and Y represent substituents on one or more
of the rings and wherein X or Y or both can be a fused aromatic
ring. In one embodiment, Y represents a fused benzene ring, such
that the organometallic complex is a facial iridium complex of
formula 5:
##STR00011##
The facial isomer of INV-19 is required for the desired blue
emission characteristics. M. Matsuura et al., in JP 2003272861,
disclose a compound having the same formula as INV-19 except that
the stereochemical isomer (facial or meridianal) is not specified.
Matsuura et al. report a green, not blue, electroluminescence from
the material. No synthetic procedure is given for how the material
was made, and no analytical characterization is provided.
Meridianal isomers typically give a broadened and red-shifted
emission relative to that of the corresponding facial isomer
(above-referenced Tamayo, et al.). Therefore, it is expected that
the meridianal isomer would produce a greener emission than the
facial isomer, as seen by Matsuura.
Suitably, the phosphorescent light-emitting layer of the OLED
device includes a host and one or more dopant compounds disposed in
the host material where the dopant(s) is/are present in an amount
of up to 15% by weight of the host, and more typically from 0.1-5.0
wt % of the host. At least one dopant is suitably a light-emitting
organometallic complex of Formula (1).
Desirable hosts are capable of forming a continuous film and the
host is selected so as to have a high level of energy transfer from
the host to the dopant material. Examples of desirable hosts useful
in this invention are nitrogen heterocyclic host compounds such as
4,4'-N,N'-dicarbazole-biphenyl (CBP),
2,2'-dimethyl-4,4'-N,N'-dicarbazole-biphenyl,
2,2'-bis(1-phenyl-1H-benzimidazol-2-yl)biphenyl, and
m-(N,N'-dicarbazole)benzene (mCP). Another class of useful hosts
include organic phosphineoxide host compounds disclosed in JP2003
317965A and JP2004 204140A, and by Ren in U.S. Patent Application
Publication No. 2006/0269784. Another class of useful hosts
includes organosilane host compounds disclosed by Ren et al. in
U.S. Patent Application Publication No. 2007/0087219.
Embodiments of the invention can provide advantageous features such
as operating efficiency, higher luminance, color hue, low drive
voltage, and improved operating stability.
Unless otherwise specifically stated, use of the term "substituted"
or "substituent" means any group or atom other than hydrogen.
Unless otherwise provided, when a group (including a compound or
complex) containing a substitutable hydrogen is referred to, it is
also intended to encompass not only the unsubstituted form, but
also further substituted derivatives with any substituent group or
groups as herein mentioned, so long as the substituent does not
destroy properties necessary for utility. Suitably, a substituent
group can be halogen or can be bonded to the remainder of the
molecule by an atom of carbon, silicon, oxygen, nitrogen,
phosphorous, sulfur, selenium, or boron. The substituent can be,
for example, halogen, such as chloro, bromo or fluoro; nitro;
hydroxyl; cyano; carboxyl; or groups which can be further
substituted, such as alkyl, including straight or branched chain or
cyclic alkyl, such as methyl, trifluoromethyl, ethyl, t-butyl,
3-(2,4-di-t-pentylphenoxy)propyl, and tetradecyl; alkenyl, such as
ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy,
butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy,
tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy, and
2-dodecyloxyethoxy; aryl such as phenyl, 4-t-butylphenyl,
2,4,6-trimethylphenyl, naphthyl; aryloxy, such as phenoxy,
2-methylphenoxy, alpha- or beta-naphthyloxy, and 4-tolyloxy;
carbonamido, such as acetamido, benzamido, butyramido,
tetradecanamido, alpha-(2,4-di-t-pentyl-phenoxy)acetamido,
alpha-(2,4-di-t-pentylphenoxy)butyramido,
alpha-(3-pentadecylphenoxy)-hexanamido,
alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido,
2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl,
N-methyltetradecanamido, N-succinimido, N-phthalimido,
2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, and
N-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino,
benzyloxycarbonylamino, hexadecyloxycarbonylamino,
2,4-di-t-butylphenoxycarbonylamino, phenylcarbonylamino,
2,5-(di-t-pentylphenyl)carbonylamino,
p-dodecyl-phenylcarbonylamino, p-tolylcarbonylamino,
N-methylureido, N,N-dimethylureido, N-methyl-N-dodecylureido,
N-hexadecylureido, N,N-dioctadecylureido,
N,N-dioctyl-N'-ethylureido, N-phenylureido, N,N-diphenylureido,
N-phenyl-N-p-tolylureido, N-(m-hexadecylphenyl)ureido,
N,N-(2,5-di-t-pentylphenyl)-N'-ethylureido, and t-butylcarbonamido;
sulfonamido, such as methylsulfonamido, benzenesulfonamido,
p-tolylsulfonamido, p-dodecylbenzenesulfonamido,
N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino, and
hexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl,
N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl,
N,N-dimethylsulfamoyl, N-[3-(dodecyloxy)propyl]sulfamoyl,
N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl,
N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl,
such as N-methylcarbamoyl, N,N-dibutylcarbamoyl,
N-octadecylcarbamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl,
N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl,
such as acetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl,
p-dodecyloxyphenoxycarbonyl methoxycarbonyl, butoxycarbonyl,
tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl,
3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such as
methoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl,
2-ethylhexyloxysulfonyl, phenoxysulfonyl,
2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl,
2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl,
phenylsulfonyl, 4-nonylphenylsulfonyl, and p-tolylsulfonyl;
sulfonyloxy, such as dodecylsulfonyloxy, and hexadecylsulfonyloxy;
sulfinyl, such as methylsulfinyl, octylsulfinyl,
2-ethylhexylsulfinyl, dodecylsulfinyl, hexadecylsulfinyl,
phenylsulfinyl, 4-nonylphenylsulfinyl, and p-tolylsulfinyl; thio,
such as ethylthio, octylthio, benzylthio, tetradecylthio,
2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio,
2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such as
acetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy,
N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and
cyclohexylcarbonyloxy; amine, such as phenylanilino,
2-chloroanilino, diethylamine, dodecylamine; imino, such as
1(N-phenylimido)ethyl, N-succinimido or 3-benzylhydantoinyl;
phosphate, such as dimethylphosphate and ethylbutylphosphate;
phosphite, such as diethyl and dihexylphosphite; a heterocyclic
group, a heterocyclic oxy group or a heterocyclic thio group, each
of which can be substituted and which contain a 3 to 7 membered
heterocyclic ring composed of carbon atoms and at least one hetero
atom selected from the group consisting of oxygen, nitrogen,
sulfur, phosphorous, or boron, such as 2-furyl, 2-thienyl,
2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such
as triethylammonium; quaternary phosphonium, such as
triphenylphosphonium; and silyloxy, such as trimethylsilyloxy.
If desired, the substituents can themselves be further substituted
one or more times with the described substituent groups. The
particular substituents used can be selected by those skilled in
the art to attain the desired properties for a specific application
and can include, for example, electron-withdrawing groups,
electron-donating groups, and steric groups. When a molecule can
have two or more substituents, the substituents can be joined
together to form a ring such as a fused ring unless otherwise
provided. Generally, the above groups and substituents thereof can
include those having up to 48 carbon atoms, typically 1 to 36
carbon atoms and usually less than 24 carbon atoms, but greater
numbers are possible depending on the particular substituents
selected.
Device
The present invention can be employed in most OLED device
configurations. These include very simple structures including a
single anode and cathode to more complex devices, such as passive
matrix displays includes orthogonal arrays of anodes and cathodes
to form pixels, and active-matrix displays where each pixel is
controlled independently, for example, with thin film transistors
(TFTs).
A typical structure, especially useful for of a small molecule
device, is shown in FIG. 1 and includes a substrate 101, an anode
103, a hole-injecting layer 105, a hole-transporting layer 107, a
light-emitting layer 109, an electron-transporting layer 111, and a
cathode 113. These layers are described in detail below. Note that
the substrate can alternatively be located adjacent to the cathode,
or the substrate can actually constitute the anode or cathode. The
organic layers between the anode and cathode are conveniently
referred to as the organic EL element. Also, the total combined
thickness of the organic layers is desirably less than 500 nm.
The anode and cathode of the OLED are connected to a
voltage/current source through electrical conductors. The OLED is
operated by applying a potential between the anode and cathode such
that the anode is at a more positive potential than the cathode.
Holes are injected into the organic EL element from the anode and
electrons are injected into the organic EL element at the cathode.
Enhanced device stability can sometimes be achieved when the OLED
is operated in an AC mode where, for some time period in the cycle,
the potential bias is reversed and no current flows. An example of
an AC driven OLED is described in U.S. Pat. No. 5,552,678.
Substrate
The OLED device of this invention is typically provided over a
supporting substrate 101 where either the cathode or anode can be
in contact with the substrate. The electrode in contact with the
substrate is conveniently referred to as the bottom electrode.
Conventionally, the bottom electrode is the anode, but this
invention is not limited to that configuration. The substrate can
either be light transmissive or opaque, depending on the intended
direction of light emission. The light transmissive property is
desirable for viewing the EL emission through the substrate.
Transparent glass or plastic is commonly employed in such cases.
The substrate can be a complex structure including multiple layers
of materials. This is typically the case for active matrix
substrates wherein TFTs are provided below the OLED layers. It is
still necessary that the substrate, at least in the emissive
pixilated areas, include largely transparent materials such as
glass or polymers. For applications where the EL emission is viewed
through the top electrode, the transmissive characteristic of the
bottom support is immaterial, and therefore can be light
transmissive, light absorbing or light reflective. Substrates for
use in this case include, but are not limited to, glass, plastic,
semiconductor materials, silicon, ceramics, and circuit board
materials. Again, the substrate can be a complex structure
including multiple layers of materials such as found in active
matrix TFT designs. It is necessary to provide in these device
configurations a light-transparent top electrode.
Anode
When the desired electroluminescent light emission (EL) is viewed
through the anode, the anode should be transparent or substantially
transparent to the emission of interest. Common transparent anode
materials used in this invention are indium-tin oxide (ITO),
indium-zinc oxide (IZO) and tin oxide, but other metal oxides can
work including, but not limited to, aluminum- or indium-doped zinc
oxide, magnesium-indium oxide, and nickel-tungsten oxide. In
addition to these oxides, metal nitrides, such as gallium nitride,
and metal selenides, such as zinc selenide, and metal sulfides,
such as zinc sulfide, can be used as the anode. For applications
where EL emission is viewed only through the cathode, the
transmissive characteristics of the anode are immaterial and any
conductive material can be used, transparent, opaque or reflective.
Example conductors for this application include, but are not
limited to, gold, iridium, molybdenum, palladium, and platinum.
Typical anode materials, transmissive or otherwise, have a work
function of 4.1 eV or greater. Desired anode materials are commonly
deposited by any suitable process such as evaporation, sputtering,
chemical vapor deposition, or electrochemical deposition. Anodes
can be patterned using well-known photolithographic processes.
Optionally, anodes can be polished prior to application of other
layers to reduce surface roughness so as to minimize shorts or
enhance reflectivity.
Hole-Injecting Layer (HIL)
While not always necessary, it is often useful that a
hole-injecting layer 105 be provided between anode 103 and
hole-transporting layer 107. The hole-injecting material can serve
to improve the film formation property of subsequent organic layers
and to facilitate injection of holes into the hole-transporting
layer. Suitable materials for use in the hole-injecting layer
include, but are not limited to, porphyrinic compounds as described
in U.S. Pat. No. 4,720,432, plasma-deposited fluorocarbon polymers
as described in U.S. Pat. No. 6,208,075, and some aromatic amines,
for example, m-MTDATA
(4,4',4''-tris[(3-methylphenyl)phenylamino]triphenylamine).
Alternative hole-injecting materials reportedly useful in organic
EL devices are described in EP 0 891 121 A1 and EP 1 029 909
A1.
Hole-Transporting Layer (HTL)
The hole-transporting layer 107 of the organic EL device contains
at least one hole-transporting compound such as an aromatic
tertiary amine, where the latter is understood to be a compound
containing at least one trivalent nitrogen atom that is bonded only
to carbon atoms, at least one of which is a member of an aromatic
ring. In one form the aromatic tertiary amine can be an arylamine,
such as a monoarylamine, diarylamine, triarylamine, or a polymeric
arylamine. Exemplary monomeric triarylamines are illustrated by
Klupfel et al. U.S. Pat. No. 3,180,730. Other suitable
triarylamines substituted with one or more vinyl radicals or
including at least one active hydrogen containing group are
disclosed by Brantley et al U.S. Pat. Nos. 3,567,450 and
3,658,520.
A more preferred class of aromatic tertiary amines are those which
include at least two aromatic tertiary amine moieties as described
in U.S. Pat. Nos. 4,720,432 and 5,061,569. Such compounds include
those represented by structural formula (A).
##STR00012## wherein Q.sub.1 and Q.sub.2 are independently selected
aromatic tertiary amine moieties and G is a linking group such as
an arylene, cycloalkylene, or alkylene group of a carbon to carbon
bond. In one embodiment, at least one of Q.sub.1 or Q.sub.2
contains a polycyclic fused ring structure, e.g., a naphthalene.
When G is an aryl group, it is conveniently a phenylene,
biphenylene, or naphthalene moiety.
A useful class of triarylamines satisfying structural formula (A)
and containing two triarylamine moieties is represented by
structural formula (B):
##STR00013## where
R.sub.1 and R.sub.2 each independently represents a hydrogen atom,
an aryl group, or an alkyl group or R.sub.1 and R.sub.2 together
represent the atoms completing a cycloalkyl group; and
R.sub.3 and R.sub.4 each independently represents an aryl group,
which is in turn substituted with a diaryl substituted amino group,
as indicated by structural formula (C):
##STR00014## wherein R.sub.5 and R.sub.6 are independently selected
aryl groups. In one embodiment, at least one of R.sub.5 or R.sub.6
contains a polycyclic fused ring structure, e.g., a
naphthalene.
Another class of aromatic tertiary amines are the
tetraaryldiamines. Desirable tetraaryldiamines include two
diarylamino groups, such as indicated by formula (C), linked
through an arylene group. Useful tetraaryldiamines include those
represented by formula (D).
##STR00015## wherein
each Are is an independently selected arylene group, such as a
phenylene or anthracene moiety,
n is an integer of from 1 to 4, and
Ar, R.sub.7, R.sub.8, and R.sub.9 are independently selected aryl
groups.
In a typical embodiment, at least one of Ar, R.sub.7, R.sub.8, and
R.sub.9 is a polycyclic fused ring structure, e.g., a
naphthalene
The various alkyl, alkylene, aryl, and arylene moieties of the
foregoing structural formulae (A), (B), (C), (D), can each in turn
be substituted. Typical substituents include alkyl groups, alkoxy
groups, aryl groups, aryloxy groups, and halogen such as fluoride,
chloride, and bromide. The various alkyl and alkylene moieties
typically contain from about 1 to 6 carbon atoms. The cycloalkyl
moieties can contain from 3 to about 10 carbon atoms, but typically
contain five, six, or seven ring carbon atoms--e.g., cyclopentyl,
cyclohexyl, and cycloheptyl ring structures. The aryl and arylene
moieties are usually phenyl and phenylene moieties.
The hole-transporting layer can be formed of a single or a mixture
of aromatic tertiary amine compounds. Specifically, one can employ
a triarylamine, such as a triarylamine satisfying the formula (B),
in combination with a tetraaryldiamine, such as indicated by
formula (D). When a triarylamine is employed in combination with a
tetraaryldiamine, the latter is positioned as a layer interposed
between the triarylamine and the electron injecting and
transporting layer. Illustrative of useful aromatic tertiary amines
are the following: 1,1-Bis(4-di-p-tolylaminophenyl)cyclohexane
1,1-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane
4,4'-Bis(diphenylamino)quadriphenyl
Bis(4-dimethylamino-2-methylphenyl)-phenylmethane
N,N,N-Tri(p-tolyl)amine
4-(di-p-tolylamino)-4'-[4(di-p-tolylamino)-styryl]stilbene
N,N,N',N'-Tetra-p-tolyl-4-4'-diaminobiphenyl
N,N,N',N'-Tetraphenyl-4,4'-diaminobiphenyl
N,N,N',N'-tetra-1-naphthyl-4,4'-diaminobiphenyl N,N,N',N
'-tetra-2-naphthyl-4,4'-diaminobiphenyl N-Phenylcarbazole
4,4'-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl
4,4'-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl
4,4''-Bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl
4,4'-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl
4,4'-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl
1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene
4,4'-Bis[N-(9-anthryl)-N-phenylamino]biphenyl
4,4''-Bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl
4,4'-Bis[N-(2-phenanthryl)-N-phenylamino]biphenyl
4,4'-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl
4,4'-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl
4,4'-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl
4,4'-Bis[N-(2-perylenyl)-N-phenylamino]biphenyl
4,4'-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl
2,6-Bis(di-p-tolylamino)naphthalene
2,6-Bis[di-(1-naphthyl)amino]naphthalene
2,6-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene
N,N,N',N'-Tetra(2-naphthyl)-4,4''-diamino-p-terphenyl
4,4'-Bis{N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl
4,4'-Bis[N-phenyl-N-(2-pyrenyl)amino]biphenyl
2,6-Bis[N,N-di(2-naphthyl)amine]fluorene
1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene
4,4',4''-tris[(3-methylphenyl)phenylamino]triphenylamine
Another class of useful hole-transporting materials includes
polycyclic aromatic compounds as described in EP 1 009 041.
Tertiary aromatic amines with more than two amine groups can be
used including oligomeric materials. In addition, polymeric
hole-transporting materials can be used such as
poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole,
polyaniline, and copolymers such as
poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) also
called PEDOT/PSS.
Light-Emitting Layer (LEL)
As more fully described in U.S. Pat. Nos. 4,769,292 and 5,935,721,
the light-emitting layer (LEL) of the organic EL element in general
includes a luminescent fluorescent or phosphorescent material where
electroluminescence is produced as a result of electron-hole pair
recombination in this region. The OLED device of this invention
includes a phosphorescent light-emitting organometallic complex as
described above. However, an OLED device of this invention can
include more than one light-emitting layer as known in the art. The
light-emitting layers can be fluorescent or phosphorescent layers
as known in the art, providing that at least one of the
light-emitting layers includes an organometallic complex as
described above. A light-emitting layer can include a single
material, but more commonly consists of a host material doped with
a guest emitting material or materials where light emission comes
primarily from the emitting materials and can be of any color. The
host materials in the light-emitting layer can be an
electron-transporting material, as defined below, a
hole-transporting material, as defined above, or another material
or combination of materials that support hole-electron
recombination. The emitting material is usually chosen from highly
fluorescent dyes and phosphorescent compounds, e.g., transition
metal complexes as described in WO 98/55561, WO 00/18851, WO
00/57676, and WO 00/70655. Emitting materials are typically
incorporated at 0.01 to 10% by weight of the host material.
The host and emitting materials can be small non-polymeric
molecules or polymeric materials such as polyfluorenes and
polyvinylarylenes (e.g., poly(p-phenylenevinylene), PPV). In the
case of polymers, small molecule emitting materials can be
molecularly dispersed into a polymeric host, or the emitting
materials can be added by copolymerizing a minor constituent into a
host polymer.
An important relationship for choosing an emitting material is a
comparison of the bandgap potential which is defined as the energy
difference between the highest occupied molecular orbital and the
lowest unoccupied molecular orbital of the molecule. For efficient
energy transfer from the host to the emitting material, a necessary
condition is that the band gap of the dopant is smaller than that
of the host material. For phosphorescent emitters it is also
important that the host triplet energy level of the host be high
enough to enable energy transfer from host to emitting
material.
Host and emitting materials known to be of use include, but are not
limited to, those disclosed in U.S. Pat. Nos. 4,768,292; 5,141,671;
5,150,006; 5,151,629; 5,405,709; 5,484,922; 5,593,788; 5,645,948;
5,683,823; 5,755,999; 5,928,802; 5,935,720; 5,935,721, and
6,020,078.
Metal complexes of 8-hydroxyquinoline and similar derivatives
(Formula E) constitute one class of useful host compounds capable
of supporting electroluminescence, and are particularly suitable
for light emission of wavelengths longer than 500 nm, e.g., green,
yellow, orange, and red.
##STR00016## wherein
M represents a metal;
n is an integer of from 1 to 4; and
Z independently in each occurrence represents the atoms completing
a nucleus having at least two fused aromatic rings.
The metal can, for example, be an alkali metal, such as lithium,
sodium, or potassium; an alkaline earth metal, such as magnesium or
calcium; an earth metal, such aluminum or gallium, or a transition
metal such as zinc or zirconium. Generally any monovalent,
divalent, trivalent, or tetravalent metal known to be a useful
chelating metal can be employed.
Z completes a heterocyclic nucleus containing at least two fused
aromatic rings, at least one of which is an azole or azine ring.
Additional rings, including both aliphatic and aromatic rings, can
be fused with the two required rings, if required. To avoid adding
molecular bulk without improving on function the number of ring
atoms is usually maintained at 18 or less.
Illustrative of useful chelated oxinoid compounds are the
following:
CO-1: Aluminum trisoxine [alias,
tris(8-quinolinolato)aluminum(III)]
CO-2: Magnesium bisoxine [alias,
bis(8-quinolinolato)magnesium(II)]
CO-3: Bis[benzo{f}-8-quinolinolato]zinc (II)
CO-4:
Bis(2-methyl-8-quinolinolato)aluminum(III)-.mu.-oxo-bis(2-methyl-8--
quinolinolato)aluminum(III)
CO-5: Indium trisoxine [alias, tris(8-quinolinolato)indium]
CO-6: Aluminum tris(5-methyloxine) [alias,
tris(5-methyl-8-quinolinolato)aluminum(III)]
CO-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)]
CO-8: Gallium oxine [alias, tris(8-quinolinolato)gallium(III)]
CO-9: Zirconium oxine [alias,
tetra(8-quinolinolato)zirconium(IV)]
Benzazole derivatives (Formula G) constitute another class of
useful host materials capable of supporting electroluminescence,
and are particularly suitable for light emission of wavelengths
longer than 400 nm, e.g., blue, green, yellow, orange or red.
##STR00017## Where:
n is an integer of 3 to 8;
Z is O, NR or S; and
R and R' are individually hydrogen; alkyl of from 1 to 24 carbon
atoms, for example, propyl, t-butyl, heptyl, and the like; aryl or
hetero-atom substituted aryl of from 5 to 20 carbon atoms for
example phenyl and naphthyl, furyl, thienyl, pyridyl, quinolinyl
and other heterocyclic systems; or halo such as chloro, fluoro; or
atoms necessary to complete a fused aromatic ring; and
L is a linkage unit consisting of alkyl, aryl, substituted alkyl,
or substituted aryl, which conjugately or unconjugately connects
the multiple benzazoles together. An example of a useful benzazole
is 2,2',2''-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole].
Distyrylarylene derivatives are also useful hosts, as described in
U.S. Pat. No. 5,121,029. Carbazole derivatives are particularly
useful hosts for phosphorescent emitters. Other useful classes of
host materials include organic phosphineoxide host compounds
disclosed by Ren in U.S. Patent Application Publication No.
2006/0269784 and organosilane host compounds disclosed by Ren et
al. in U.S. Patent Application Publication No. 2007/0087219.
Electron-Transporting Layer (ETL)
Preferred thin film-forming materials for use in forming the
electron-transporting layer 111 of the organic EL devices of this
invention are metal chelated oxinoid compounds, including chelates
of oxine itself (also commonly referred to as 8-quinolinol or
8-hydroxyquinoline). Such compounds help to inject and transport
electrons and exhibit both high levels of performance and are
readily fabricated in the form of thin films. Exemplary of
contemplated oxinoid compounds are those satisfying structural
formula (E), previously described.
Other electron-transporting materials include various butadiene
derivatives as disclosed in U.S. Pat. No. 4,356,429 and various
heterocyclic optical brighteners as described in U.S. Pat. No.
4,539,507. Benzazoles satisfying structural formula (G) are also
useful electron transporting materials. Triazines are also known to
be useful as electron transporting materials.
In addition to suitable hosts, an OLED device employing a
phosphorescent material often requires at least one exciton,
electron, or hole blocking layer to help confine the excitons,
electrons, or electron-hole recombination centers to the
light-emitting layer including the host and phosphorescent
material. In one embodiment, such a blocking layer would be placed
between electron-transporting layer 111 and light-emitting layer
109. In this case, the ionization potential of the blocking layer
should be such that there is an energy barrier for hole migration
from the host into the electron-transporting layer, while the
electron affinity should be such that electrons pass more readily
from the electron-transporting layer into the light-emitting layer
including host and phosphorescent material. It is further desired,
but not absolutely required, that the triplet energy of the
blocking material be greater than that of the phosphorescent
material. Suitable hole-blocking materials are described in U.S.
Patent Application Publication Nos. 2002/0015859; 2003/0068528;
2003/0175553 and WO 00/70655; WO 01/93642. Two examples of useful
materials are bathocuproine (BCP) and
bis(2-methyl-8-quinolinolato)(4-phenylphenolato)Aluminum(III)
(BAlQ). Metal complexes other than BAlQ are also known to block
holes and excitons as described in U.S. Patent Application
Publication No. 2003/0068528. U.S. Patent Application Publication
No. 2003/0175553 describes the use of
fac-tris(1-phenylpyrazolato-N,C.sup.2')iridium(III) (Irppz) in an
electron/exciton blocking layer. Another useful electron/exciton
blocking material is 4,4',4''-tris-(N-carbazolyl)triphenylamine
(TCTA). Other useful classes of hole-blocking materials include
organic phosphineoxide host compounds disclosed by Ren in U.S.
Patent Application Publication No. 2006/0269784 and organosilane
host compounds disclosed by Ren et al. in U.S. Patent Application
Publication No. 2007/0087219.
Cathode
When light emission is viewed solely through the anode, the cathode
used in this invention can include nearly any conductive material.
Desirable materials have good film-forming properties to ensure
good contact with the underlying organic layer, promote electron
injection at low voltage, and have good stability. Useful cathode
materials often contain a low work function metal (<4.0 eV) or
metal alloy. One useful cathode material includes a Mg:Ag alloy
wherein the percentage of silver is in the range of 1 to 20%, as
described in U.S. Pat. No. 4,885,221. Another suitable class of
cathode materials includes bilayers including the cathode and a
thin electron-injection layer (EIL) in contact with an organic
layer (e.g., an electron transporting layer (ETL)) which is capped
with a thicker layer of a conductive metal. Here, the EIL
preferably includes a low work function metal or metal salt, and if
so, the thicker capping layer does not need to have a low work
function. One such cathode includes a thin layer of LiF followed by
a thicker layer of Al as described in U.S. Pat. No. 5,677,572.
Other useful cathode material sets include, but are not limited to,
those disclosed in U.S. Pat. Nos. 5,059,861; 5,059,862, and
6,140,763.
When light emission is viewed through the cathode, the cathode must
be transparent or nearly transparent. For such applications, metals
must be thin or one must use transparent conductive oxides, or a
combination of these materials. Optically transparent cathodes have
been described in more detail in U.S. Pat. Nos. 4,885,211;
5,247,190; 5,703,436; 5,608,287; 5,837,391; 5,677,572; 5,776,622;
5,776,623; 5,714,838; 5,969,474; 5,739,545; 5,981,306; 6,137,223;
6,140,763; 6,172,459; 6,278,236; 6,284,3936 and EP 1 076 368 and JP
3,234,963. Cathode materials are typically deposited by any
suitable method such as evaporation, sputtering, or chemical vapor
deposition. When needed, patterning can be achieved through many
well known methods including, but not limited to, through-mask
deposition, integral shadow masking as described in U.S. Pat. No.
5,276,380 and EP 0 732 868, laser ablation, and selective chemical
vapor deposition.
Other Useful Organic Layers and Device Architecture
In some instances, layers 109 and 111 can optionally be collapsed
into a single layer that serves the function of supporting both
light emission and electron transportation. Additionally, a single
layer can function to block holes or excitons, and also support
electron transportation. It also known in the art that emitting
materials can be included in the hole-transporting layer, which can
serve as a host. Multiple materials can be added to one or more
layers in order to create a white-emitting OLED, for example, by
combining blue- and yellow-emitting materials, cyan- and
red-emitting materials, or red-, green-, and blue-emitting
materials. White-emitting devices are described, for example, in EP
1 187 235, U.S. Patent Application Publication No. 2002/0025419, EP
1 182 244, U.S. Pat. Nos. 5,683,823; 5,503,910; 5,405,709 and
5,283,182 and can be equipped with a suitable filter arrangement to
produce a color emission.
This invention can be used in so-called stacked device
architecture, for example, as taught in U.S. Pat. Nos. 5,703,436
and 6,337,492.
Deposition of Organic Layers
The organic materials mentioned above are suitably deposited by any
process suitable for the form of the organic materials. In the case
of small molecules, they are conveniently deposited through
sublimation, but can be deposited by other processes such as from a
solvent with an optional binder to improve film formation. If the
material is a polymer, solvent deposition is usually preferred. The
material to be deposited by sublimation can be vaporized from a
sublimator "boat" often includes a tantalum material, e.g., as
described in U.S. Pat. No. 6,237,529, or can be first coated onto a
donor sheet and then sublimed in closer proximity to the substrate.
Layers with a mixture of materials can utilize separate sublimator
boats or the materials can be pre-mixed and coated from a single
boat or donor sheet. Patterned deposition can be achieved using
shadow masks, integral shadow masks (U.S. Pat. No. 5,294,870),
spatially-defined thermal dye transfer from a donor sheet (U.S.
Pat. Nos. 5,688,551; 5,851,709 and 6,066,357) and inkjet method
(U.S. Pat. No. 6,066,357).
Encapsulation
Most OLED devices are sensitive to moisture or oxygen, or both, so
they are commonly sealed in an inert atmosphere such as nitrogen or
argon, along with a desiccant such as alumina, bauxite, calcium
sulfate, clays, silica gel, zeolites, alkaline metal oxides,
alkaline earth metal oxides, sulfates, or metal halides and
perchlorates. Methods for encapsulation and desiccation include,
but are not limited to, those described in U.S. Pat. No. 6,226,890.
In addition, barrier layers such as SiOx, Teflon, and alternating
inorganic/polymeric layers are known in the art for
encapsulation.
Optical Optimization
OLED devices of this invention can employ various well-known
optical effects in order to enhance its properties if desired. This
includes optimizing layer thicknesses to yield maximum light
transmission, providing dielectric mirror structures, replacing
reflective electrodes with light-absorbing electrodes, providing
anti-glare or anti-reflection coatings over the display, providing
a polarizing medium over the display, or providing colored, neutral
density, or color-conversion filters over the display. Filters,
polarizers, and anti-glare or anti-reflection coatings can be
specifically provided over the cover or as part of the cover.
Synthesis of the emitting materials useful in the invention can be
accomplished by preparing the organic ligand and then using a metal
to complex the ligand and form the organometallic compound. The
synthesis of ligands useful in the invention can be accomplished by
various methods found in the literature.
SYNTHETIC EXAMPLE 1
Preparation of Inv-1
##STR00018##
The cyclometalated Ir(III) .mu.-chloro-bridged dimer was prepared
by refluxing IrCl.sub.3.nH.sub.2O with 2.2 equiv. of
2-phenylpyridine (ppy) in a 3:1 mixture of 2-ethoxyethanol and
water for 12 hours. The precipitate was collected by filtration and
washed with water, a small amount of methanol, and ether. It was
then dried in a warm vacuum oven.
The chloro-bridged dimer complex (1 g) and silver triflate (0.5 g)
were placed in a 100 ml round bottomed flask with 20 ml of
acetonitrile and the mixture was degassed, and then refluxed for 4
hours under a nitrogen atmosphere. After cooling, the yellow
solution was filtered to remove insoluble material. The solvent was
removed under vacuum and the intermediate
bis(acetonitrile)bis[(2-phenylpyridinato-N,C.sup.2')]iridium(III)
triflate was recovered.
Bis(acetonitrile)bis[(ppy)]iridium(III) triflate and
1-(2-pyridinyl)-1H-benzimidazole (2.5 equiv, prepared according to
the method in J. Org. Chem., 71(21), 8324-7, 2006) were placed in a
100 ml round bottomed flask with 35 ml of 1,2-propanediol. The
mixture was degassed, and then refluxed for 12 hours under nitrogen
atmosphere. After cooling, the precipitate was collected by
filtration, washed with ethanol, redissolved in dichloromethane,
and then chromatographed with dichloromethane plus 5% methanol. MS:
m/z calcd 695; found 696 [M+1]. HPLC indicated about 96% purity.
Further purification was carried out by sublimation. Single-crystal
X-ray analysis revealed that INV-1 as prepared herein has a facial
configuration. The compound gave a blue emission in solution (see
FIG. 2).
SYNTHETIC EXAMPLE 2
Preparation of Inv-2
##STR00019##
The cyclometalated Ir(III) .mu.-chloro-bridged dimer was prepared
by refluxing IrCl.sub.3.nH.sub.2O with 2.2 equiv. of
2-(1,4-difluorophenyl)pyridine (dfppy) in a 3:1 mixture of
2-ethoxyethanol and water for 12 hours. The precipitate was
collected by filtration and washed with water, a small amount of
methanol, and ether. It was then dried in a warm vacuum oven.
The chloro-bridged dimer complex (1.14 g) and silver triflate (0.5
g) were placed in a 100 ml round bottomed flask with 20 ml of
acetonitrile. The mixture was degassed, and then refluxed for 4
hours under a nitrogen atmosphere. After cooling, the yellow
solution was filtered to remove insoluble material and the solvent
was removed under vacuum, leaving the intermediate
bis(acetonitrile)bis[((4',6'-difluorophenyl)pyridine-N,C.sup.2')]iridium(-
III) triflate.
Bis(acetonitrile)bis[(dfppy)]iridium(III) triflate and
1-(2-pyridinyl)-1H-benzimidazole (2.5 equiv) were placed in a 100
ml round bottomed flask with 35 ml of 1,2-propanediol and the
mixture was degassed, and then refluxed for 12 hours under nitrogen
atmosphere. After cooling, the precipitate was collected by
filtration, washed with water, redissolved in dichloromethane, and
then chromatographed with dichloromethane plus 2.5% methanol. MS:
m/z calcd 767; found 768 [M+1]. HPLC indicated about 90% purity.
Further purification was carried out by sublimation. The compound
gave a blue emission in solution (see FIG. 2).
SYNTHETIC EXAMPLE 3
Preparation of Inv-19
##STR00020##
Bis(1,5-cyclooctadiene)iridium (I) tetrafluoroborate (0.52 g) and
1-(2-pyridinyl)-1H-benzimidazole (1.1 mL) were taken up in
1,2-propanediol (30 mL) and the mixture freeze/thaw degassed. The
mixture was then heated to reflux for 4 hours. The mixture was
cooled to room temperature and the off-white precipitate collected
and washed with water and dried. The solid was then dissolved in
minimal amount of 9:1 dichloromethane and methanol, and the
solution was left in the refrigerator for recrystallization. A
white powder was subsequently collected. MS: m/z calcd 775; found
776 [M+1]. .sup.1H NMR (in 1,1,2,2-tetrachloroethane-d.sub.2): 6.70
(1H, d), 7.03 (1H, dd), 7.20 (1H, dd), 7.62 (1H, dd), 7.73 (1H, d),
7.84 (1H, d), 8.36 (1H, d), 8.50 (1H, dd). The NMR spectrum is
shown in FIG. 3. The simple NMR spectrum shows that all three
ligands in the complex are equivalent (related by symmetry), thus
proving that the compound obtained is the facial isomer, not the
meridianal isomer. The compound gave a blue emission in DMSO
solution (see FIG. 2). INV-19 is clearly the facial isomer of the
chemical formula shown.
The invention and its advantages can be better appreciated by the
following examples.
DEVICE EXAMPLES 1-1 to 1-3
A series of EL devices satisfying the requirements of the invention
was constructed in the following manner: 1. OLED devices were
fabricated on .about.1.1-mm-thick glass substrates precoated with a
transparent indium-tin oxide (ITO) conductive layer having a
thickness of .about.22 nm and a sheet resistance of .about.70
.OMEGA./square. The substrates were cleaned and dried using a
commercial glass scrubber tool, and were then treated with oxygen
plasma. 2. Over the ITO was deposited a 1 nm fluorocarbon (CFx)
hole-injecting layer (HIL) by plasma-assisted deposition of
CHF.sub.3. 3. A hole-transporting layer (HTL) of
N,N'-di-1-naphthyl-N,N'-diphenyl-4,4'-diaminobiphenyl (NPB) having
a thickness of 90 nm was then evaporated from a tantalum boat. 4. A
10 nm electron-blocking layer (EBL) of
4,4',4''-tris-(N-carbazolyl)triphenylamine (TCTA) was then
deposited onto the hole-transporting layer by evaporation from a
tantalum boat. 5. A 20 nm light-emitting layer (LEL) of
m-bis(N-carbazole)benzene (mCP) and Inv-2 was then deposited onto
the electron-blocking layer. These materials were also evaporated
from tantalum boats. The weight % of Inv-2 was from 6% to 10%, as
shown in Table 1, below. 6. A hole-blocking layer of
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) having a
thickness of 40 nm was then evaporated from a tantalum boat. 7. A
0.5 nm lithium fluoride (LiF) electron-injecting layer was
deposited over the hole-blocking layer. 8. On top of the LiF layer
was deposited a 150 nm aluminum cathode.
The device was then hermetically packaged in a dry glove box for
protection against ambient environment.
TABLE-US-00001 TABLE 1 Evaluation Results for EL devices 1-1 to
1-3. Phos- pho- rescent External Power emitter Voltage, quantum
efficiency, Device Wt. % V Yield, % lm/W CIEx CIEy 1-1 6 7.36 1.44
1.05 0.1493 0.2500 1-2 8 6.90 1.84 1.42 0.1484 0.2488 1-3 10 7.34
2.19 1.59 0.1482 0.2491
DEVICE EXAMPLES 2-1 to 2-4
A series of EL devices satisfying the requirements of the invention
was constructed in the following manner: 1. OLED devices were
fabricated on .about.1.1-mm-thick glass substrates precoated with a
transparent indium-tin oxide (ITO) conductive layer having a
thickness of .about.22 nm and a sheet resistance of .about.70
.OMEGA./square. The substrates were cleaned and dried using a
commercial glass scrubber tool, and were then treated with oxygen
plasma. 2. Over the ITO was deposited a 1 nm fluorocarbon (CFx)
hole-injecting layer (HIL) by plasma-assisted deposition of
CHF.sub.3. 3. A hole-transporting layer (HTL) of NPB having a
thickness of 75 nm was then evaporated from a tantalum boat. 4. A
10 nm electron-blocking layer (EBL) of TCTA was then deposited onto
the hole-transporting layer by evaporation from a tantalum boat. 5.
A 35 nm light-emitting layer (LEL) of mCP and
2,2'-bis(1-phenyl-1H-benzimidazol-2-yl)biphenyl (PBB) with 10%
Inv-2 was then deposited onto the electron-blocking layer. These
materials were also evaporated from tantalum boats. The weight % of
mCP was from 0% to 45%, as shown in Table 2, below. 6. A 10 nm
electron-transporting layer (ETL) of PBB was then deposited onto
the light-emitting layer. This material was also evaporated from a
tantalum boat. 7. A hole-blocking layer of BCP having a thickness
of 25 nm was then evaporated from a tantalum boat. 8. A 0.5 nm
lithium fluoride (LiF) electron-injecting layer of was deposited
over the hole-blocking layer. 9. On top of the LiF layer was
deposited a 1000 nm aluminum cathode.
The device was then hermetically packaged in a dry glove box for
protection against ambient environment.
TABLE-US-00002 TABLE 2 Evaluation Results for EL devices 2-1 to
2-4. External Power mCP Voltage, quantum efficiency, Device Wt. % V
Yield, % lm/W CIEx CIEy 2-1 0 8.64 7.27 4.36 0.1440 0.2376 2-2 15
7.26 7.39 5.20 0.1434 0.2333 2-3 30 6.49 7.92 6.22 0.1435 0.2337
2-4 45 6.22 8.76 7.27 0.1434 0.2368
DEVICE EXAMPLES 3-1 to 3-4
A series of EL devices satisfying the requirements of the invention
was constructed as described above for Examples 2-1 to 2-4, except
that Steps 5 and 6 were as follows: 5. A 35 nm light-emitting layer
(LEL) of mCP and 2,6-pyridylbis(diphenylphosphineoxide) (PDP) with
10% Inv-2 were then deposited onto the electron-blocking layer.
These materials were also evaporated from tantalum boats. The
weight % of mCP was from 0% to 45%, as shown in Table 3, below. 6.
A 10 nm electron-transporting layer (ETL) of PDP was then deposited
onto the light-emitting layer. This material was also evaporated
from a tantalum boat.
TABLE-US-00003 TABLE 3 Evaluation Results for EL devices 3-1 to
3-4. External Power mCP Voltage, quantum efficiency, Device Wt. % V
Yield, % lm/W CIEx CIEy 3-1 0 8.48 1.64 1.03 0.1529 0.2453 3-2 15
7.93 3.54 2.54 0.1531 0.2704 3-3 30 6.86 4.12 4.45 0.1545 0.2743
3-4 45 6.37 3.94 3.55 0.1550 0.2743
DEVICE EXAMPLES 4-1 to 4-5
A series of EL devices satisfying the requirements of the invention
was constructed as described above for Examples 2-1 to 2-4, except
that Steps 5 and 6 were as follows: 5. A 35 nm light-emitting layer
(LEL) of mCP and bis(4-dimesitylboronphenyl)diphenylsilane (MBPS)
with 10% Inv-2 was then deposited onto the electron-blocking layer.
These materials were also evaporated from tantalum boats. The
weight % of mCP was from 0% to 60%, as shown in Table 4, below. 6.
A 10 nm electron-transporting layer (ETL) of MBPS was then
deposited onto the light-emitting layer. This material was also
evaporated from a tantalum boat.
TABLE-US-00004 TABLE 4 Evaluation Results for EL devices 4-1 to
4-4. External Power mCP Voltage, quantum efficiency, Device Wt. % V
Yield, % lm/W CIEx CIEy 4-1 0 11.8 0.83 0.43 0.1733 0.3016 4-2 15
8.29 4.17 2.88 0.1539 0.2719 4-3 30 7.37 4.93 3.87 0.1563 0.2751
4-4 45 7.07 5.07 4.16 0.1578 0.2770 4-5 60 6.51 6.83 6.07 0.1572
0.2747
As can be seen from the results in the above tables, OLED devices
of this invention including a mixed-ligand organometallic complex
as described herein can provide blue emission with good voltage
requirements. Some of the devices also have very good quantum
yields and power efficiency, in particular devices 2-1 to 2-4 and
4-4 to 4-5. FIG. 4 shows the EL spectrum characteristics of device
2-4. This device demonstrates a rare example of highly efficient
tris-(C^N) cyclometalated Ir(II)-based OLEDs with "deep blue"
emission.
The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
TABLE-US-00005 PARTS LIST 101 Substrate 103 Anode 105
Hole-Injecting layer (HIL) 107 Hole-Transporting layer (HTL) 109
Light-Emitting layer (LEL) 111 Electron-Transporting layer (ETL)
113 Cathode
* * * * *